Cooling arrangements for molten metals



July 16, 1963 Filed Sept. 17, 1959 T. R A. DAVEY ETAL COOLING ARRANGEMENTS FOR MOLTEN METALS 2 Sheets-Sheet l y 1963 T. R. A. DAVEY ETAL 3,098,110

COOLING ARRANGEMENTS FOR MOLTEN METALS Filed Sept. 17, 1959 r 2 Sheets-Sheet 2 United States Patent 3,098,110 COOLING ARRANGEMENTS FDR MOLTEN METALS Thomas Ronald Albert Davey, Bristol, and Walter Lindsay Linton, Langford, near Bristol, England, assiguors to Metallurgical Processes Limited, Nassau, Bahamas, and The National Smelling Company Limited, London, England, doing business together as Metallurgical Development Company, Nassau, Bahamas Filed Sept. 17, 1959, Ser. No. 840,600 Claims priority, application Great Britain (lot. 17, 1958 Claims. (Cl. 266-) This invention relates to the cooling of the zinc-containing molten lead in zinc vapor condensing systems in which zinc vapor is condensed in molten lead circulating successively through the condenser, a cooling device, a settling zone and back to the condenser, and has for its object the provision of certain improvements in cooling the zinc-containing molten lead withdrawn from the condenser.

In the smelting of zinciferous materials for the production of metallic zinc, as for example in a zinc-smelting blast furnace, the zinc vapor in the smelting gases is commonly condensed in molten lead circulating through the condenser in countercurrent with the flow therethrough of the gases. The molten lead with its burden of condensed zinc passes from the condenser to a cooling device where the temperature is lowered to promote the separation of zinc from the molten mixture of lead and zinc. The molten metal mixture then passes to a settling zone or tank where molten metallic zinc is removed by overflow, continuously or periodically, and the residual molten lead, still containing some zinc, is returned to the condenser where the cycle is repeated. The present invention is concerned with apparatus for facilitating the cooling of the zinc-rich molten lead passing from the condenser to the settling zone.

In accordance with the present invention the cooling arrangement for the zinc-rich molten lead comprises a suitable cooling chamber, such as a trough or tank, through which the molten metal mixture passes and which is provided with one or more interiorly cooled rotating drums, or the like, arranged to dip into the molten metal mixture for extracting heat therefrom. Each drum is interiorly cooled by passing a cooling fluid therethrough, the flow of cooling fluid being coordinated with the speed of rotation of the drum to inhibit solidification of lead on the surface of the drum. The cooling drum is generally cylindroid in shape and is mounted for rotation in a generally vertical axis. The drum is adapted to be substantially completely immersed, or immersed for the greater part of its length, in the zinc-containing molten lead in the cooling chamber or tank, and the drum is provided with stationary internal baflles that tend to prevent rotation of the body of cooling fluid within the drum due to rotation of the drum.

. Preferably means are also provided for preventing the molten metal which is to be cooled, from being agitated or rotated by the drum, said means, for example, consisting of a circular skirt which dips into the metal and from which depend a number of vertical baflles or blades.

The invention will be best understood from the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic plan of a zinc vapor condensing system embodying the invention, the upper portion of the supporting structure of each of the cooling drums being cut off along line 1-1 of FIG. 2 in order to show the cooling drums more clearly,

FIGURE 2 is a vertical section taken on the section line 22 of FIGURE 1, and

FIGURE 3 is a horizontal section taken on the section line 3--3 of FIGURE 2.

FIGURE 4 shows part of FIGURE 2 showing a modification.

The gaseous product of the zinc-smelting operation flows through the condenser 5 in counter-current with the molten lead circulating therethrough. The molten lead with its burden of condensed zinc is Withdrawn from the gas intake end of the condenser into a sump or the like 6. A pump 7 transfers the zinc-rich molten lead from the sump through a pipe 8 into the cooling tank 9, where the molten metal mixture is cooled by contact with the rotating drums Ill, and gradually separates into a layer of zinc-containing lead 11 (see FIGURE 2) with a lead-containing zinc layer 12 floating on top, and above that a protective layer 13 of flux such as zinc ammonium chloride. The cooled molten metal mixture is delivered to a settling tank 14 from whence the floating layer of zinc is removed by overflow into a zinc holding tank 15. The de-zinced molten lead is returned through a pipe 16 to the gas outlet end of the condenser 5. The cooling tank 9 is surrounded by an outer case 17, and gas burners or the like 18 are provided at convenient positions between the tank 9 and the outer case 17 to heat the space therebetween, whenever it is necessary to supply external heat to the tank in order to prevent undue cooling of the circulating molten lead, more particularly when the condenser is temporarily out of action.

Referring to FIGURE 2, each cooling drum 10 is cylindroid in shape and preferably made of sheet steel. The drum is mounted to rotate about a generally vertical axis, and its circular top is of slightly greater diameter than its bottom. An upright tubular extension neck 19 communicates with the interior of the drum through a circular hole in the top thereof, the extensions being welded or otherwise suitably secured to the top of the drum with the vertical axes of the drum and extension coincident. The extension 19 is rotatably supported in bearings 20, thus serving as the shaft for the rotatable drum. The vertical thrust of the water-filled drum and extension upon the bearings 20 is practically negligible because of the buoyancy imparted to the drum by its almost complete immersion in the molten metal. The drum and extension are adapted to be rotated by a powerdriven belt 21 operatively engaging a pulley 22 secured to the extension.

A suitably supported stationary pipe 23 is positioned inside the tubular extension 19. The top of the pipe is connected to a source of cooling fluid (not shown), and its lower end terminates in a discharge nozzle 24. The upper end of the rotatable extension 19 has a tonguegroove sealing connection 25 with a stationary overflow trough 26 having a lateral discharge outlet 27 for spent cooling fluid. Before the drum is closed, a series of circumferentially spaced vertical baffles or blades 28 are secured to the lower end of the stationary pipe 23 so as to be within the drum when closed.

Externally to the rotating drum is arranged a concentric circular skirt 29 which dips into the metal and from which depend a number of radial vertical baffles or blades 30. The circular skirt 29 is securely attached to a structure 32 which also supports the bearings 20.

The drum (or drums) 10 dips into the molten metal mixture in the cooling tank 9 with the top of the drum slightly above the surface of the flux layer 13-, as indicated in FlGURE 2. The drum is thus immersed for the greater part of its length in the molten metal mixture in the cooling tank. Water, or other suitable cooling fluid, is delivered to the drum through the pipe 23 and is discharged over the seal 25 into the trough 26, and is customarily returned to the source of cooling fluid for reuse. The drum is rotated at a speed sufficient to prevent solidification and adhesion of lead on the surface of the drum, other conditions of cooling being constant. Such other conditions affecting the cooling action include the initial temperature of the cooling fluid and the rate of flow of cooling fluid through the drum. Since these other conditions are in practice more or less fixed by the source and rate of supply of the cooling fluid and the dimensions of the drum and its appurtenances, the cooling action is conveniently controlled and regulated by adjusting the speed of rotation of the drum.

In operation, the water (or other cooling fluid) circulates as shown by the arrows in FIGURE 2, and is prevented from rotating with the drum so that the rotating wall of the drum has a high velocity with respect to both the molten metal and the cooling fluid, thus ensuring high heat transfer rates. Rotation of the drum about a generally vertical axis permits the circulating cooling fluid to completely fill the drum and practically complete immersion of the drum beneath the surface of the flux layer thereby attaining optimum heat transmission between the surface of the drum and the cooling fluid. The flux layer prevents the formation of aerated dross, The stationary vertical baffles within the drum minimize rotation of the cooling fluid with the drum. Rapid circulation of the cooling fluid is provided in planes passing through the axis of rotation of the drum. This also improves the heat transmission between the drum and the cooling fluid. Good circulation of cooling fluid over the end of the drum that is submerged in the'molten metal avoids localized steam formation which results in a hammering effect.

The cooling action of the drum is illustrated by this example:

With an eight-inch outside diameter drum of fit-inch wall thickness immersed about 6 inches in the lead (surface area 1.4 sq. ft.) and rotated at 300 r.p.m. and with 20-30 gal./min. water at about 15 C. initially, passed into the drum through a two-inch diameter pipe, cooling of 600,000 to 250,000 B.t.u. per hour is possible, according to depth of accretion on the drum.

The slightly conical form of the drum permits ready periodical removal of accretions which are largely zinc arsenide where the zinc vapor is condensed in a leadsplash condenser associated with a zinc smelting blast furnace.

Any solidification of lead on the drum surface indicates that too great artificial cooling of the molten metal is taking place in the immediate vicinity of the drum with attendant danger of unduly cooling the entire bath of molten metal in the cooling tank. In an elongated cooling tank or trough, cooling of the molten metal is progressive from the inlet to the outlet end of the tank, and in practice the overall cooling action will normally reduce the temperature of the molten metal from about 550 C. at the inlet end of the tank to about 450 C. at the outlet end of the tank. In other words, the artificial cooling action of the drum should be so controlled and regulated that the molten metal in the tank should not be cooled below about 450 C.

FIGURE 4 shows the drum immersed in the molten metal. In this method of operation, the neck and upper surface of the drum are provided with insulation 31 to prevent any accretion forming at these points.

We claim:

1. In the combination of a condenser in which zinc vapor is condensed in molten lead that is circulated successively through the condenser, through a cooling tank having cooling means for cooling the zinc-containing molten lead, through a settling zone where molten metallic zinc is separated and removed, the molten lead then being returned to the condenser, the improvement in said cooling means which comprises at least one generally cylindroid cooling drum rotatably mounted for rotation about the generally vertically disposed longitudinal axis of the drum, said drum being adapted to be substantially completely immersed in the zinc-containing molten lead in the cooling tank, an upright tubular extension secured to the drum and communicating with the interior thereof through a hole in the top of the drum, means for introducing cooling fluid into the drum and for withdrawing cooling fluid therefrom through said tubular extension, means for rotating the tubular extension and the drum secured thereto, means for preventing substantial rotation of cooling fluid in the drum, caused by rotation of the drum, comprising at least one radially-disposed stationary baffle positioned within the rotatable cooling drum, and means for preventing substantial rotation of the zinccontaining molten lead in the cooling tank immediately surrounding the rotatable cooling drum comprising at least one batfle extending in a direction generally vertically and radially with respect to said drum.

2. The apparatus according to claim 1 in which the means for introducing cooling fluid into the rotatable cooling drum is a vertically disposed stationary fluid supply pipe positioned within the tubular extension of the drum, and in which the circumferentially spaced stationary balfles within the drum are secured to the lower portion of the cooling fluid supply pipe.

3. The apparatus according to claim 1 in which the top of the cooling drum and the portion of the tubular extension adjacent thereto are provided with a layer of insulating material whereby the formation of accretions of solidified metal at this point is prevented.

4. The apparatus according to claim 1 in which means are provided for applying external heat to the cooling tank.

5. In the combination of a condenser in which zinc vapor is condensed in molten lead that is circulated successively through the condenser, through a cooling tank having cooling means for cooling the zinc-containing molten lead, through a settling zone where molten metallic zinc is separated and removed, the molten lead then being returned to the condenser, the improvement in said cooling means which comprises at least one generally cylindroid cooling drum rotatably mounted for rotation about the generally vertically disposed longitudinal axis of the drum, said drum being adapted to be substantially completely immersed in the zinc-containing molten lead in the cooling tank, an upright tubular extension secured to the drum and communicating with the interior thereof through a hole in the top of the drum, means for introducing cooling fluid into the drum and for withdrawing cooling fluid therefrom through said tubular extension, means for rotating the tubular extension and the drum secured thereto, and means for preventing substantial rotation of cooling fluid in the drum, caused by rotation of the drum, comprising at least one radially-disposed stationary baffle positioned within the rotatable cooling drum and having a substantially planar face facing countercurrent to the direction of rotation of said drum.

References Cited in the file of this patent UNITED STATES PATENTS 2,018,266 Kemmer Oct. 22, 1935 2,351,489 Cooper June 13, 1944 2,439,216 McLellan Apr. 6, 1948 2,734,819 Williams Feb. 14, 1956 2,801,162 Keeping July 30, 1957 2,866,702 Batutis et al Dec. 30, 1958 2,871,007 Derham et al Jan. 15, 1960 2,956,871 Curnow et al Oct. 18, 1960 FOREIGN PATENTS 563,916 Belgium Ian. 31, 1958 563,917 Belgium Jan. 31, 1958 774,269 Great Britain May 8, 1957 812,837 Great Britain May 6, 1959 

1. IN THE COMBINATION OF A CONDENSER IN WHICH ZINC VAPOR IS CONDENSED IN MOLTEN LEAD THAT IS CIRCULATED SUCCESSIVELY THROUGH THE CONDENSER, THROUGH A COOLING TANK HAVING COOLING MEANS FOR COOLING THE ZINC-CONTAINING MOLTEN LEAD, THROUGH A SETTLING ZONE WHERE MOLTEN METALLIC ZINC IS SEPARATED AND REMOVED, THE MOLTEN LEAD THEN BEING RETURNED TO THE CONDENSER, THE IMPROVEMENT IN SAID COOLING MEANS WHICH COMPRISES AT LEAST ONE GENERALLY CYLINDROID COOLING DRUM ROTATABLY MOUNTED FOR ROTATION ABOUT THE GENERALLY VERTICALLY DISPOSED LONGITUDINAL AXIS OF THE DRUM, SAID DRUM BEING ADAPTED TO BE SUBSTANTIALLY COMPLETELY IMMERSED IN THE ZINC-CONTAINING MOLTEN LEAD IN THE COOLING TANK, AN UPRIGHT TUBULAR EXTENSION SECURED TO THE DRUM AND COMMUNICATING WITH THE INTERIOR THEREOF 